In recent years light emitting diodes (LEDs) have made a grand entrance into mainstream applications. According to some studies, in 2009 alone, the worldwide sales of LEDs totaled over $5 billion. One reason for LEDs popularity over traditional incandescent bulbs is because LEDs are a more efficient source of light than incandescent bulbs. Many countries around the world have passed or will pass laws eventually banning production of or restricting the sale of incandescent bulbs. Meanwhile LEDs continue to increase in popularity. However, the fact remains that an incandescent bulb can output more light than an LED.
The Sep. 21, 2009 issue of “EE Times” is focused on LED technologies. In that publication, an article by Nicolas Mokhoff entitled, “Era of LED Lighting Dawns White,” states that “[w]hen the incandescent lamp replaced the wax candle as a light source, it changed the way humanity conducted everyday—and night-activities . . . . This year marks the dawn of a new age in lighting: that of the white LED, a brighter, more efficient way to light our lives. Lighting applications based on solid-state light sources are making headway towards replacing incandescent- and fluorescent-based lighting apps . . . . In the short run, as LED replacement lamps become a viable alternative, regulators are encouraging the use of compact fluorescent lamps (CFLs). However, lighting experts contend that over the next five years the advantages of LED technology over CFLs will be recognized, especially with respect to the quality of the light, dimming features, controllability, lamp life and environmental cost of ownership . . . . LED lamps will be used for directed-light applications, in hard-to-reach applications and where the cost of replacement is very high . . . . Eventually, solid-state LED lighting might replace traditional incandescent or fluorescent solutions in virtually all commercial and consumer applications.”
In that same publication of “EE Times,” Christoph Hammerschmidt states in an article entitled, “Auto OEMs Switch On the High Beams for LED Apps,” that “the design issues for LED headlights are not trivial. Some kind of temperature control for the headlight unit is required; designer are still debating the relative merits of fans and heat sinks. Further, with up to 80 LEDs crammed into one unit, contact reliability must be high enough not to cancel out the reliability gained by switching to LEDs. And both OEMs and carmakers bemoan the lack of standards for LED lighting, in particular for packaging.”
Furthermore, in that same publication of “EE Times,” an article by Bolaji Ojo entitled, “Shedding Light on the LED Distribution Chain,” states that “‘[a] lot of traditional lighting fixture companies, in the past, never had electronic engineers on staff. There was never a need for it.’ said Arrow's Gatza. ‘As the evolution of lighting has taken place, companies have needed to have engineers on staff who understand not only how you get the LEDs into the product, but also how to select the drivers for the LEDs.’ Distributors today advise lighting companies . . . on such matters as what type of IC driver to install, whether to select an IC module or go the software route with a driver solution, how to choose among power supplies, what kind of thermal management system to use, and how to ensure the right products are selected and optimized to meet time-to-market goals.”
In addition, in that same publication of “EE Times,” Yolchiro Hata states in an article entitled, “Color-adjustable LED Lamps For Residential Market Get Aggressive on Price,” that “Sharp added a light-color adjuster to its residential LED bulbs to address consumers' reservations about LED color performance, said Hironori Taniguchi of the Sharp LED center's product planning department. ‘We place three 2,800 K color-temperature LEDs and three 5,000 K color-temperature LEDs inside the bulb,’ Taniguchi said. ‘Remote control adjusts the output ratio of each color-temperature LED. We implemented artifacts to create “daylight white” at 5,000 K by combining a blue LED element and a yellow fluorescent gas. To create the “classic white” bulb color at a 2,800 K color temperature, we combined a blue LED element with red fluorescent and green fluorescent gases.’”
Also in that same publication of “EE Times,” Bill Schweber states in an article entitled, “LED Reality: Simple Devices, Complex Considerations,” that “[t]he LED circuit designer has to balance conflicting objectives . . . . First, of course, is the power source itself: How much current does it have to provide, and how good (stable and perhaps even programmable) does it have to be? If the LEDs have to be dimmed, should that be done by simple analog control of the current level or by pulse-width modulation with a variable duty cycle? Many applications require more optical output than a single LED can provide, or need a wider-area light source, such as for backlighting a display. Such designs can be accomplished with multiple LEDs, but there are many trade-offs in the topology of the multi-LED arrangement. Designers can choose basic serial string, a parallel grouping or a series/parallel combination. The trade-offs include accommodating a possible LED failure in a series path; deciding between a single-source power supply and multiple, smaller supplies; and considering the compliance voltage required of the current source as the voltage drops across the LEDs in a string. Then there's the heat. Certainly, LEDs are much more efficient than any other commercially available light source, converting between 60 and 80 percent of the electrical input into useful output (compared with roughly 10 percent for an incandescent bulb.) But the power that an LED doesn't use for light translates to heat, which remains in the LED die (in an old-fashioned incandescent bulb, of course, the wasteful dissipation is radiated out. As a consequence, designers must often plan for thermal management of LED-based illumination . . . [s]olutions can involve basic heat sinks, passive or forced airflow, pc board copper areas and even more-extensive schemes . . . . The focus turns to colorimetry and photometry—the LED's light itself- and this worry takes on various dimensions. LED output tends to dim with age (they last a long time, but they do age) so you have to make sure you'll have enough light output over your product's lifetime. The wave-length (color output) of an LED also changes with its drive level, which is a factor in some applications . . . . Factors [in measuring optical power] include which wavelengths (colors) to include, over what solid angle, and how to handle the dispersed output over that solid angle (LED output is directional, of course).”
In addition, LED window candles are known in the art. Such LED window candles may provide for wax or a wax-like covering on the sidewall of the candle housing to simulate a candle. Moreover, these electronic simulated candles may include a flame-shaped glass bulb to further simulate a candle, and the LED may produce amber light to better resemble the color of candle light. The LED window candle may be powered by a battery-powered solar recharging lighting system. In another example, the light emission levels from the LED may be varied to simulate the flicker of candle light. However, prior art LED window candles are deficient in various aspects and improvement thereof are desirable.